A search engine may be used to locate particular documents in a collection of documents. In addition, a search engine may be used to locate particular keywords or phrases in a document. Search engines may use one or more indices to locate particular documents, keywords, or phrases. In addition, search engines may perform Boolean and other operations in the course of locating particular information. Search engines may require significant time to perform a search. Indices that reduce the time required to perform a search are generally beneficial.